The present invention relates to a swash plate type variable displacement compressor.
Japanese Unexamined Patent Application Publication No. 52-131204 discloses a swash plate type variable displacement compressor (hereinafter, referred to as compressor). The compressor includes a housing having therein a suction chamber, a discharge chamber, a swash plate chamber, and a plurality of cylinder bores. A drive shaft is rotatably supported in the housing. The swash plate chamber accommodates therein a swash plate that is rotatable with the drive shaft. The swash plate has a circular shape and has an insertion hole at the center thereof. A link mechanism that allows a change in the inclination angle of the swash plate is disposed between the drive shaft and the swash plate. The inclination angle herein refers to an angle of the swash plate with respect to a plane extending perpendicular to the rotational axis of the drive shaft.
Each cylinder bore accommodates a reciprocally movable piston and thus forms a compression chamber with the piston. A conversion mechanism is provided that converts the rotation of the swash plate into reciprocal movement of each piston in its associated cylinder bore with a stroke length corresponding to the inclination angle of the swash plate. The compressor further includes an actuator that changes the inclination angle of the swash plate and a control mechanism that controls the actuator.
The link mechanism includes a lug member and an arm. The lug member is fixed on the drive shaft in the swash plate chamber on the front side of the swash plate. The arm is swingably connected to the lug member and the swash plate through a connecting pin. The arm transmits the rotation of the lug member to the swash plate and allows a change in the inclination angle of the swash plate while the top dead center position of the swash plate being maintained.
The actuator includes the lug member and a movable body that is integrally rotatably engaged with the swash plate and moves in the direction of the axis of rotation so as to change the inclination angle of the swash plate. Specifically, the lug member has a columnar shape and is concentric with the axis of rotation and a cylinder chamber in which the movable body is movable. The cylinder chamber is defined by the movable body to thereby form a pressure control chamber and the movable body is moved by the pressure in the pressure control chamber. The swash plate has in the insertion hole thereof a hinge ball. The hinge ball is mounted on the swash plate to allow the swash plate to pivot about the drive shaft. The rear end of the movable body is in contact with the hinge ball. A pressing spring is provided on the rear side of the hinge ball for urging the hinge ball in the direction that increases the inclination angle of the swash plate.
The control mechanism includes a control passage and a control valve. The control passage includes a pressure-changing passage that is in communication with the pressure control chamber, a low-pressure passage that is in communication with the suction chamber and the swash plate chamber, and a high-pressure passage that communicates with the discharge chamber. A part of the pressure-changing passage is formed in the drive shaft. The control valve controls the opening of the pressure-changing passage, the low-pressure passage, and the high-pressure passage. In other words, the control valve provides communication between the pressure-changing passage and the low-pressure passage or between the pressure-changing passage and the high-pressure passage.
In the compressor, when the communication between the pressure-changing passage and the high-pressure passage is allowed through the control valve, the pressure in the pressure control chamber becomes higher than that of the swash plate chamber. This causes the movable body of the actuator to move away from the lug member and presses the hinge ball rearward in the swash plate chamber. As a result, the inclination angle of the swash plate is reduced to reduce the stroke length of the pistons and hence the displacement of the compressor. When the communication between the pressure-changing passage and the low-pressure passage is allowed through the control valve, on the other hand, the pressure in the pressure control chamber is lowered to a level almost equal to the pressure level of the pressure in the swash plate chamber. This causes the movable body of the actuator to move toward the lug member. The urging force of the pressing spring acts on the hinge ball to move the hinge ball following the movable body, which increases the inclination angle of the swash plate. Accordingly, the stroke length of the pistons and hence the displacement of the compressor is increased. When the inclination angle of the swash plate is maximum, the swash plate is in contact with the rear end of the lug member.
In order to ensure a high controllability of the compressor, the swash plate may have a balancing weight for controlling the inertia generated by the rotation of the swash plate. Such balancing weight may extend in the direction that is opposite to the position of the top dead center of the swash plate, i.e., extend from the swash plate side toward the lug member side.
In this configuration, when the inclination angle of the swash plate is maximum, the balancing weight is in contact with the rear end of the lug member, which means that the compressor needs to be longer in the axial direction.
The present invention, which has been made in view of the circumstances above, and is directed to providing a swash plate type variable displacement compressor that is small in size and ensures a high controllability.